A third generation mobile communication system (3G) standardized by Third Generation Partnership Project (3GPP) includes a base station and a Radio Network Controller (RNC) that controls the base station as a host apparatus of the base station in a radio network. Stream Control Transmission Protocol (SCTP) is used as one of protocols for controlling communications between the base station and the RNC. Third generation (3G) mobile communication standards include Long Term Evolution (LTE) and LTE-A (LTE-Advanced) as improved version of the LTE. In the LTE and the LTE-A, SCTP-based communications are performed between the base station and Mobility Management Entity (MME) as a host apparatus of the base station.
For example, a given base station establishes a communication path (called a connection or a session) based on the SCTP with the host apparatus, and receives data from the host apparatus via the communication path. On the other hand, the base station establishes an SCTP-based communication path with another base station, and transfers the data received from the host apparatus via this communication path. According to a terminology of the SCTP, the communication path is called an “association ”.
According to the SCTP, the communications are performed on an exchange unit called a “chunk ” ,and an arrival sequence of the chunks containing transmission target data (which are called DATA chunks) is guaranteed between the transmission and the reception. Therefore, e.g., a data reception side transmits a SACK (Selective Acknowledgement) chunk, indicating that the data is successfully received, back to a data transmission side. The transmission side refers to a content of the SACK chunk, and retransmits the data not yet arriving at the reception side.
For further information, see Japanese Laid-Open Patent Publication No. 2012-109975. Japanese National Publication of International Patent Application No. 2005-520436.
The base station described above operates as a relay apparatus to relay the data between the host apparatus and another base station, in which case it may happen that a communication environment between the base station and another base station is lower in quality than a communication environment between the base station and host apparatus. For example, a band usable for the communications via the association between the base station and another base station is narrower than a band usable for the communications via the association between the host apparatus and the base station as the case may be.
In this case, such a problem arises as to cause an increase in capacity of a memory used for the base station to store transfer target data given from the host apparatus in order to absorb a difference an quantity of data received from the host apparatus per unit time and a quantity of data that can be transmitted to another base station per unit time. The data stored in the memory cannot be deleted from the memory unless the reception of the data from another base station is permitted through the SACK chunk in preparation for a retransmission request given from another base station. Consequently, under a condition having a poor communication quality between the base station and another base station and having frequent retransmissions of the data, the base station continues storing the data in the memory in preparation for the data retransmission. The memory capacity held by the base station further increases when taking such a case into consideration.